This invention relates to a separately derived isolated ground interface apparatus, and more particularly, to a power interface box for connecting isolated ground (IG) receptacles at a termination point remote from the main electrical service entrance of the facility.
Isolated ground receptacles, typically orange in color, are used with critical electronic systems to provide a separate ground reference point from the safety or chassis ground required to protect personnel from short circuit voltages in the conduit/raceway system. Critical electronic systems include, but are not limited to, point of sale networks, fueling management systems, computer networks, telecom systems, security systems, automatic teller machines (ATM), internet kiosks, and self checkout point of sale networks.
Typically, an isolated ground conductor must be routed back to the electrical service entrance grounding terminal of a facility exposing the isolated ground conductor to electrical contamination (noise) by induced voltages from other parallel current carrying conductors that are run in the same conduits, raceways, and panelboards. This electrical contamination compromises the true isolation of the isolated ground conductor thereby reducing its effectiveness.
The electrical contamination can cause damage, non-operation, or misoperation of electronic components as a result of poor isolation in the grounding path. Thus, there exists a need for a separate termination point for the isolated ground conductor remote of the main service entrance to prevent electrical contamination.
The National Electrical Code (NEC) allows for alternate wiring of the isolated ground conductor to terminate at a separately derived apparatus. A separately derived apparatus is produced by using an isolation transformer which has separate primary and secondary windings used to provide protection from common mode electrical contamination. The isolation transformer provides an inductive cushion by establishing a neutral to ground bond. This bond prevents the formation and transmission of common mode voltages to electrical devices, such as the critical electronic systems listed above. The separately derived apparatus, therefore, can be used to eliminate electrical contamination associated with long runs of an isolated ground conductor.
The present invention addresses these problems by providing a separately derived isolated ground interface apparatus utilizing a power interface box capable of providing an interface between the isolation transformer and the remote, hard wired isolated ground receptacles. Thus, the isolated ground interface apparatus provides isolated ground receptacles with a separately derived isolated ground free of electrical contamination.